Some postmenopausal women rapidly lose postcranial bone, and estrogen replacement therapy (ERT) can reduce this loss. Since 1993, the applicant has studied healthy postmenopausal women in a prospective, double-blind, placebo-controlled investigation to determine if the rate of postcranial bone loss is related to the rate of alveolar bone loss and to determine the effect of ERT on bone-loss rates at these sites. Initial results indicate that alveolar bone loss is correlated with postcranial bone loss and that alveolar bone loss increases with years since menopause, cigarette smoking and parity. To further understand the effect of hormonal replacement therapy as a preventive measure for alveolar and postcranial bone loss in postmenopausal women, the applicant proposes to test the hypothesis that HRT that arrests or reduces the rate of postcranial bone deterioration after menopause will similarly affect alveolar bone loss, and thus prevent or delay loss of teeth. An open-label ERT study is proposed for two years on the cohort of postmenopausal women currently enrolled in the ongoing trial. The long term protective effect of ERT on postcranial and alveolar bone will be evaluated as a function of bone loss rates. The filmless photostimulable phosphor plate (PSP) technology will be used and validated for quantitative measurement of alveolar bone mass. Preliminary studies indicate that PSP technology offers significant advantages over current film-based methods including sensitivity and quantitation. If the protective effect of HRT is related to the rate of alveolar bone loss, then a simple, routine dental visit may identify subjects that would most benefit from postmenopausal HRT. This study will assay effective interventions that can delay or prevent tooth loss in elderly women, an important dental public health problem.